Electron beam system and method of manufacturing devices using the system

ABSTRACT

An electron beam system wherein a shot noise of an electron beam can be reduced and a beam current can be made higher, and further a shaped beam is formed by a two-stage lenses so as to allow for an operation with high stability. In this electron beam system, an electron beam emitted from an electron gun is irradiated onto a sample and secondary electrons emanated from the sample are detected. The electron gun is a thermionic emission type and designed to operate in a space charge limited condition. A shaping aperture and a NA aperture are arranged in front locations of the electron gun. An image of the shaping aperture formed by an electron beam emitted from the thermionic emission electron gun is focused onto a surface of the sample through the two-stage lenses.

BACKGROUND OF THE INVENTION

The present invention relates to an electron beam system, a defectinspection apparatus for a device, which employs the same electron beamsystem, and a manufacturing method of a device using the same defectinspection apparatus, and more specifically, relates to an electron beamsystem which can evaluate a sample (a semiconductor wafer) having adevice pattern with a minimum line width equal to or less than 0.1 μmwith both a high throughput and high reliability, a defect inspectionapparatus for a device, which employs the same electron beam system, anda manufacturing method of a device which can improve a yield thereof byevaluating a wafer after it has been processed using the same defectinspection apparatus.

The present invention also relates to an electron beam system and adefect inspection method for evaluating a device, such as a wafer or amask, having a pattern with a minimum line width in a range of 0.1micron, and also to a method for manufacturing a device with a highyield by using the same system and a defect inspection method.

The present invention further relates to a method for simplifying aregistration (positioning) of an inspection apparatus in which anelectron beam is irradiated against a sample and secondary electronsemanated from the sample are detected and then processed to therebyobtain an SEM (Scanning Electron Microscope) image of a fine geometry ona surface of the sample, and thus carry out evaluation thereof. The finegeometry on the sample surface may be, for example, on a semiconductorwafer or a mask having a high-density pattern with a minimum line widthequal to or less than 0.1 μm. The present invention also relates to amanufacturing method of a semiconductor device using such an inspectionapparatus.

One such electron beam system has been suggested for evaluating a samplehaving a device pattern with a minimum line width equal to or less than0.1 μm, in which a shaped electron beam is demagnified (contracted) tobe narrower and irradiated onto a sample and then secondary electronsemanated from the sample are detected so as to evaluate the sample. Insuch a system, an optical system for shaping the electron beam hasemployed at least a three-stage of lenses. Besides, when it is intendedto form such a narrow electron beam equal to or less than 0.1 μm, ademagnification crossover image type beam has been employed. Further, itis required to increase an intensity of the electron beam in order toprovide evaluation with higher reliability, and in this case athermoelectric field emission (schottky) cathode electron gun has beenused so as to obtain a high current beam of 0.1 μm or smaller.

Such an electron beam system has been known, in which a primary electronbeam emitted from an electron gun is demagnified to be narrower so as toirradiate a sample, such as a wafer or a mask, and a secondary electronbeam, which has been emanated from the sample through this irradiation,is detected, to thereby detect any defects or to measure a line width onthe sample. Further, it has been also known that an electron beam isirradiated on a sample and thereby charges are introduced to a patternon the sample so as to induce a voltage, which is in turn measured andthus an electric parameter of the sample is measured.

In the prior art, for measuring the voltage induced in the pattern onthe surface of the sample, there has been employed one such method inwhich a hemispherical mesh filter is provided, and the secondaryelectrons emanated from the sample surface are returned to the samplesurface side or introduced into a detector arranged behind the mesh independence on a potential of the pattern from which the secondaryelectrons have been emanated, thus carrying out measurement of thepotential of the pattern. An electron gun in an electron beam system tobe used in such a method may be in most cases one designated as aschottky type by Zr—W having a magnified intensity. Further, ademagnified crossover image formed by the electron gun has been commonlyused as a probe current for injecting charges into the sample to measurethe voltage of the pattern.

One such inspection apparatus has been well known that uses a scanningelectron microscope to inspect a subject (sample), such as asemiconductor wafer and so on. In this inspection apparatus, a narrowlydemagnified electron beam is used to conduct raster scanning with araster scanning width of an extremely narrow space, and then secondaryelectrons emanated from the subject are detected by a detector so as toform an SEM image, wherein two SEM images for corresponding locations intwo different samples are compared to each other to detect any defects.

A lithography apparatus which comprises an electron optical system andwhich uses an electron beam to form a fine geometry on a surface of asample such as a semiconductor wafer requires position alignment or aregistration of high precision between the electron optical system andthe sample. In order to satisfy this requirement, one method has beenemployed that uses the electron optical system of the lithographyapparatus to detect an alignment mark on the sample to accomplish theposition alignment, and also another method has been employed, in whichan optical microscope is further provided in addition to the electronoptical system so as to perform rough alignment (a roughly controlledposition alignment) through an observation across an enlarged field ofview by using the optical microscope and also fine alignment (a highmagnification position alignment) by using the electron optical systemof the lithography apparatus. However, such high precision alignment isnot necessarily required in an inspection apparatus.

SUMMARY OF THE INVENTION

However, it is problematic that although in a schottky electron gun, abeam current three to ten times higher as compared to that obtained by athermionic emission electron gun (e.g., LaB₆ electron gun) can beobtained, and a shot noise of the electron beam is quite large andinevitably an S/N ratio is not so good, which makes it difficult toevaluate a sample with high throughput.

On the other hand, the crossover image demagnification type beam byusing the LaB₆ electron gun also has a drawback such that it isimpossible to make the beam current higher, and this makes it difficultto evaluate a sample with high throughput.

Further, in the method for shaping a beam by using the LaB₆ electrongun, since it uses three or more stage of lenses, a long optical columnmust be used and a deflector is additionally required for axialalignment. It is also problematic that the space charge effect becomesgreater in proportion to the length of the optical path, and it isdifficult to accomplish a good intensity and position stability of theelectron beam.

One of the subjects to be accomplished by the invention is to provide anelectron beam system that can provide an evaluation of a sample withhigh throughput by reducing a shot noise of an electron beam and therebyimproving the S/N ratio.

Another subject to be accomplished by the present invention is toprovide an electron beam system that allows a beam current to be madehigher and thus can evaluate a sample with high throughput.

Still another subject to be accomplished by the present invention is toprovide a fully furnished system for a defect inspection apparatus bymanufacturing an electron optical column employing only two stage oflenses to form and control a shaped beam with high stability.

Yet another subject to be accomplished by the present invention is toprovide a manufacturing method of a device, in which a sample afterhaving been processed is evaluated by using the electron beam system asdescribed above.

An electron beam system according to the prior art is associated withthe problems stated above, in addition to the problem that the systemtends to be too complicated, and also that since the filter made up ofhemispherical mesh used in a measurement of the potential contrast formsa non-axisymmetric electric field, an uncorrectable distortion may beinduced in a measured result. Besides, since the electron gun of theschottky cathode type produces a big shot noise, it is required to applya high beam current or to emit an intensified primary electron beam inorder to obtain a good S/N ratio. Further, if the magnified crossoverimage is used as the above-stated probe current and an electron gunhaving the same intensity is used in this case, then again,problematically, the beam current would be smaller as compared to a casein using the demagnified image of the shaping aperture.

The present invention has been made to solve the problems pointed outabove, and the object thereof is to provide an electron beam systemwhich comprises an axisymmetric filter as well as an electron gun with asmaller shot noise, and allows a relatively higher beam current to beobtained as compared to that which can be achieved by using an electrongun with the same brightness, and also to provide a defect inspectionmethod using the same electron beam system, as well as a devicemanufacturing method using the same electron beam system and defectinspection method.

There has been a problem that if both rough alignment and fine alignmentare carried out, it takes a long time to complete an alignmentoperation, resulting in a lower throughput (a quantity of processing perunit time) achieved by the inspection apparatus. In addition, when anelectron optical system is used to conduct alignment, an electron beamdose equivalent to or greater than that applied in the sample evaluationwould be applied to the wafer, which in turn could destroy a gate oxideor the like. The present invention is also directed to solving the aboveproblem. Accordingly, another object of the present invention is toprovide an inspection apparatus, in which inspection of a wafer can becarried out by conducting alignment without using any electron beams,and thus without destroying the gate oxide and the like. Another objectof the present invention is to provide a device manufacturing methodusing such an inspection apparatus as described above.

The above-described subjects are solved by the following means. That is,the present invention provides an electron beam system, in which anelectron beam emitted from an electron gun is irradiated onto a sampleand secondary electrons emanated from the sample are detected, whereinsaid electron gun is specified to be a thermionic emission electron gun,and a shaping aperture and a NA aperture are arranged in front locationsof said thermionic emission electron gun, wherein an image of theshaping aperture irradiated by the electron beam from said thermionicemission electron gun is formed on a surface of the sample by two-stagelenses. It is to be noted that the expression “in (a) front location(s)of” is defined as in the sample side which is (are) in a forward sidewith respect to the direction along which the electrons advance. Asecondary electron beam includes a reflected electron reflected by thesample surface, a transmission electron having transmitted through thesample, and an emanated electron emanated from the sample by theirradiation of the primary electron beam.

Further, according to one aspect of the present invention, there isprovided an electron beam system in which an electron beam emitted froman electron gun is irradiated onto a sample and secondary electronsemanated from the sample are detected, wherein said electron gun isspecified to be a thermionic emission electron gun and a shapingaperture and a NA aperture are arranged in front locations of saidthermionic emission electron gun, wherein a crossover image formed bythe electron beam from the thermionic electron gun is formed into animage in the NA aperture, and an image of the shaping apertureirradiated by the electron beam from the thermionic emission electrongun is formed on a surface of the sample.

Further, according to another aspect of the present invention, there isprovided an electron beam system which has a primary optical system forirradiating an electron beam emitted from the electron gun onto a sampleand in which secondary electrons emanated from a surface of the sampleare detected by a detector, the system being characterized in that ashaping aperture and two-stage lenses are arranged in the primaryoptical system, and additionally, an E×B separator is arranged betweenthe two-atage lenses, wherein an image of a shaping aperture irradiatedby an electron beam from said electron gun is demagnified and formed onthe sample surface by the two-stage lenses and secondary electronsemanated from the sample surface are separated by said E×B separatorfrom the primary optical system and introduced into a detector.

According to still another aspect of the present invention, there isprovided an electron beam system which has a primary optical system forirradiating an electron beam emitted from an electron gun onto a sampleand in which secondary electrons emanated from a surface of the sampleare detected by a detector, the system being characterized in that theprimary optical system comprises a shaping aperture, a NA aperture, acondenser lens and an objective lens disposed in a sequential manneralong an optical axis of the primary optical system, wherein a crossoverimage of the electron beam from the electron gun is focused to the NAaperture by controlling a Wehnelt bias (an electrode bias) of theelectron gun.

According to yet another aspect of the present invention, provided is anelectron beam system which has a primary optical system for irradiatingan electron beam emitted from an electron gun onto a sample and in whichsecondary electrons emanated from a surface of the sample are detectedby a detector, the system being characterized in that the primaryoptical system comprises a shaping aperture, a condenser lens and anobjective lens disposed in a sequential manner along an optical axis ofthe primary optical system, and a NA aperture is disposed in a locationadjacent to the objective lens in the electron gun side with respect tothe objective lens, wherein a crossover image of the electron beam isformed in the NA aperture.

According to still another aspect of the present invention, there isprovided a defect inspection apparatus for a device, which is equippedwith an electron beam system as defined according to any one of theabove-described inventions or other inventions. Further, according tothe present invention, there is provided a device manufacturing methodin which a wafer after having been processed is evaluated by using theabove described defect inspection apparatus.

An electron beam system according to the present invention scans asample surface by a primary electron beam emitted from an electron gunand then detects a secondary electron beam emanated from the sample. Inthis electron beam system, an objective lens is arranged for focusingthe primary electron beam and for accelerating the secondary electronbeam, wherein the objective lens has a plurality of electrodes.Preferably, the electron gun is operated in a space charge limitedcondition, meaning that a shot noise reduction coefficient is smallerthan 1, and a voltage applied to a plurality of electrodes of theobjective lens can be set to a desired value. Further, a demagnificationratio of the electron beam can be changed between a case for irradiatingthe electron beam against the sample so as to form a topographical or amaterial image of the sample surface, and another case for measuring apotential of a pattern formed on the sample.

Whether or not the electron gun operates in the space charge limitedzone (condition) can be examined by referring to the attached drawings,FIGS. 14(a) and 14(b) and by using a method described below. FIG. 14(a)is a graph illustrating a relationship between an electron gun currentand a cathode heating current, wherein in zone P, the electron guncurrent increase only by a small amount even if the cathode heatingcurrent is increased, which means that the zone P corresponds to thespace charge limited condition. FIG. 14(b) is a graph illustrating arelationship between the electron gun current and an anode voltage,wherein in zone Q, the electron gun current increases sharply when theanode voltage is increased, which means that the zone Q also correspondsto the space charge limited condition. From the above description, itcan be determined that the electron gun is operating in the space chargelimited condition either when the cathode heating current is increasedto measure the electron gun current thereby determining the P zone wherethe electron gun current is saturated, or when the anode voltage isincreased to measure the electron gun current thereby determining the Qzone where the electron gun current is changing sharply. Accordingly, itis possible to set the condition for operating the electron gun in thespace charge limited condition.

A defect inspection method using an electron beam system according tothe present invention comprises: an image acquiring step for irradiatingan electron beam emitted from the electron gun against the sample viathe objective lens to obtain an image of a sample surface; a measuringstep for measuring a potential or a variation thereof on the surface ofthe sample, which has been induced by irradiation of the electron beam;and a determining step for determining whether a specific pattern isgood or not based on the potential or a variation thereof. In the imageacquiring step and the measuring step, a voltage to be applied to anelectrode most proximal to the sample among the plurality of electrodesof the objective lens may be changed.

Preferably, a defect inspection method of the present inventioncomprises: a step for forming an SEM image by the scanning, and thenmeasuring and storing a position of a specific pattern on the sample;and a measuring step for measuring a potential of the pattern by theselective scanning or irradiation on said specific pattern, wherein itis examined from a result of measurement of the potential of thespecific pattern whether or not there is a defect in the sample.

Preferably, a defect inspection method of the present inventioncomprises a step for acquiring an SEM image by the scanning and a stepfor measuring a potential of a pattern, wherein in the acquiring stepand the measuring step, at least one of an excitation voltage of theobjective lens, a landing voltage (energy) to the sample and a cathodevoltage of the electron gun may be changed. The present inventionfurther provides a device manufacturing method in which a wafer isevaluated at the end of each one of the processes for manufacturing thewafer by using either the electron beam system or the defect inspectionmethod described above.

An inspection apparatus for evaluating a fine geometry on a surface of asample according to the present invention comprises: an electron opticalsystem including a primary optical system for irradiating an electronbeam against a sample and a detecting system for detecting the electronbeam emanated from the sample; a movable stage for carrying the sampleand moving the sample relative to the electron optical system; and aposition sensor capable of measuring a position of the sample with adesired precision. The position sensor is disposed in a location spacedby a desired distance from the electron optical system, and the movablestage is moved on the basis of a position signal output from theposition sensor so as to bring the sample into a reference position insaid electron optical system with a desired precision. The inspectionapparatus, in the condition where the sample has been matched to thereference position in the electron optical system with the desiredprecision, acquires an SEM image of a surface of the sample by theelectron optical system and the thus acquired SEM image is compared toanother acquired SEM image or to a reference image for the patternmatching, thereby allowing for competitive evaluation.

In the present invention, preferably, comparative evaluation isconducted by applying a pattern matching between an SEM image acquiredfrom one segment on one sample and another SEM image acquired from acorresponding segment on a different sample. Alternatively, the SEMimage acquired from one segment on one sample may be compared with areference image for the pattern matching, thus carrying out thecomparative evaluation. The position sensor measures the position of thesample by measuring an electrostatic capacity. Further, in an inspectionapparatus of the present invention, pattern matching is applied betweenthe SEM image and the reference image to provide a comparativeevaluation by performing one of translation, rotation or magnificationtuning of the image.

An inspection apparatus for evaluating a fine geometry on a surface of asample according to the present invention comprises: an electron opticalsystem consisting of a primary optical system for irradiating anelectron beam against the sample and a detecting system for detecting anelectron beam emanated from the sample; a movable stage for carrying andmoving the sample relatively with respect to the electron opticalsystem; and a position sensor disposed in a location spaced by apredetermined distance from the electron optical system and beingcapable of measuring the position of the sample with a desiredprecision. In the inspection apparatus of the present invention, themovable stage is actuated on the basis of a position signal output fromthe position sensor to bring the sample into a reference position in theelectron optical system. The inspection apparatus, in a condition thatthe sample has been matched to the reference position in the electronoptical system with a desired precision, acquires an SEM image of asurface of the sample by the electron optical system, calculates adifference between an area to be evaluated on the sample surface and afield of view of the electron optical system based on the acquired SEMimage, and then corrects the thus calculated difference by the deflectorso as to acquire the SEM image.

Further, in an inspection apparatus of the present invention, patternmatching is applied between the SEM image and the reference image toprovide a comparative evaluation by performing one of translation,rotation or magnification tuning of the image. In a device manufacturingmethod of the present invention, a wafer in the course of processing isevaluated by using one of the inspection apparatuses as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general schematic diagram of an optical system of anelectron beam system according to a first embodiment of the presentinvention;

FIG. 2 is a general schematic diagram of an optical system of anelectron beam system according to a second embodiment of the presentinvention;

FIG. 3 is a schematic diagram of one exemplary configuration of anelectron optical system in an electron beam system according to thepresent invention;

FIG. 4 is a diagram for illustrating a defect inspection carried out byusing the electron beam system of FIG. 3;

FIG. 5 is a sectional view showing a physical relationship between anobjective lens and a sample in an electron beam system of FIG. 3,illustrating only a left half thereof with respect to an optical axis;

FIG. 6 is a diagram showing a simulation result indicative of the factthat a potential contrast can be measured by using the electron beamsystem of FIG. 3;

FIG. 7 is a flow chart of a method for manufacturing a semiconductordevice by employing an electron beam system according to the presentinvention;

FIG. 8 is a flow chart of a lithography process included as asub-process in a wafer processing process shown in FIG. 7;

FIG. 9 is general schematic diagram showing an arrangement of anelectrostatic capacity sensor in an electron beam system according to anembodiment of the present invention;

FIG. 10 a is an SEM image including a field of view 521 acquired by anelectron optical system while FIG. 10 b is a reference image including afield of view 522, and FIG. 10 c is a plan view showing an example of acorner of a pattern;

FIG. 11 is a general schematic diagram of an electron beam system (anelectron optical system) according to an embodiment of the presentinvention;

FIG. 12 is a general schematic diagram of an electron beam system(mainly, a movable table) according to an embodiment of the presentinvention;

FIG. 13 a is a plan view showing a physical relationship between anelectrode of a position sensor and a wafer, while FIG. 13 b is a sideview showing a physical relationship between the electrode of theposition sensor and the wafer as well as a block diagram of respectivecomponents; and

FIG. 14 a is a graph illustrating a relationship between an electron guncurrent and a cathode current, while FIG. 14 b is a graph illustrating arelationship between an electron gun current and an anode voltage.

EXPLANATION OF REFERENCE SIGNS

The components and elements used herein are designated as follows:

1, 1′: Electron beam system, 10, 10′: Primary optical system, 11:Electron gun, 12: Electrostatic deflector (for axial alignment), 13:Shaping aperture, 14, 15: Electrostatic deflector (for axial alignment),16: NA aperture, 17: Condenser lens, 18: Electrostatic deflector, 19:E×B separator, 20: Objective lens, 21: Axisymmetric electrode, 22, 23:Power supply, 24: Shift switch, 25: Electrostatic deflector, 30:Secondary optical system, 40, 40′: Detector, 71: Optical column, 73: XYstage, 74: X table, 77: Y table, 83: Linear motor, 87: Irradiationspace, 91: Flexible pipe, 98: Exhaust pipe, 201: Cathode, 202: Wehnelt,203: Anode, 204: First condenser lens, 205: Second aperture plate, 206:First aperture plate, 207: Second condenser lens, 208: Objective lens,210: E×B separator, 211: Shield barrel, 212: Secondary electrondetector, X: Optical axis, 401, 401′: detector, 402: A/D converter, 403:Image processing circuit, 502 a, 502 b, 502 c, 505: Electrostaticcapacity sensor, 503: Periphery, 504: Notch, 510, 521, 522: Field ofview, 525-528: Pattern corner of SEM image, 525′-528′: Pattern corner ofreference image, 529: Defect, 531: Arc, 535: Optical axis, 536: Primaryoptical system, 538: Detecting system, 539: Optical axis, 540: Positionsensor, 541: Electrode, 542: Overlapped portion, 546: Electrostaticcapacity measuring instrument, 547: Comparison chart, 548: Positiondetector, 600: Electron beam system, 601: Electron gun, 603: Condenserlens, 607: First multi-aperture plate, 609: Demagnifying lens, 610:Narrow gap, 615: Sample, 619: E×B separator, 623, 625: Magnifying lens,627: Second multi-aperture plate, 629: Detector, 631: Amplifier, 628:Stop, 633: Image processing section, 635: Deflector, 637: Knife edge,639: Am meter, 643: CPU, 645: Storage, 649: Output means, A, B, P:Optical axis, C: Electron beam, G: Center of gravity of wafer, and S:Sample (Wafer).

EMBODIMENTS OF THE INVENTION

A first embodiment of an electron beam system according to the presentinvention will now be described in detail with reference to the attacheddrawings. FIG. 1 schematically shows an electron beam system 1 accordingto a first embodiment of the present invention. This electron beamsystem 1 comprises a primary optical system 10, a secondary opticalsystem 30 and a detecting system 40. The primary optical system 10serves as an optical system for irradiating an electron beam onto asample “S”, and comprises an electron gun 11 for emitting the electronbeam, an electrostatic deflector 12 used for an axial alignment, ashaping aperture 13, electrostatic deflectors 14, 15 used for the axialalignment, a NA aperture, a condenser lens 17 for demagnifying theelectron beam after passing through the shaping aperture 13, anelectrostatic deflector 18 used for scanning, an E×B separator 19, anobjective lens 20 and an axisymmetric electrode 21, all of which arearranged in a sequential manner with the electron gun 11 placed at thetop most location in a manner such that an optical axis “A” of theelectron beam emitted from the electron gun may be normal to a surface“S” of the sample. The E×B separator 19 is constituted of anelectrostatic deflector 191, electromagnetic deflectors 192, 193 and apermalloy core 194. The electron beam system 1 further comprises a powersupply 22 for applying a negative potential to the sample S.

In the first embodiment, the electron gun 11 is implemented as a LaB₆electron gun of the thermionic emission type, which comprises a LaB₆cathode 111, a graphite heater 112, a support fittings 113, a Wehneltelectrode 114 and an anode 115. By adjusting a bias of the Wehneltelectrode 114 of the electron gun 11 to be deeper to some extent, theelectron gun 11 can be controlled within a space charge limitedcondition. The shaping aperture 13 is square in shape and disposed in alocation in the electron gun side with respect to the NA aperture 16.Further, both of the two-stage lenses (i.e., the condenser lens 17 andthe objective lens 20) are disposed in front locations of the shapingaperture 13 and the NA aperture 16 (i.e., in the sample side which is ina forward side with respect to the direction along which the electronbeam advances).

The secondary optical system 30 is serving as an optical system forintroducing secondary electrons emanated from the sample S into thedetector 40, and disposed along the optical axis “B” angled with respectto the optical axis “A”, starting from a point proximal to the E×Bseparator 19. The detecting system 40 comprises a detector 401.

An operation of the electron beam system 1 configured as stated abovewill now be described.

An electron beam “C” emitted from the electron gun 11 may form acrossover image “C₁” in a location corresponding to that of the NAaperture 16 by adjusting the Wehnelt voltage of the electron gun 11. Atthe same time, the electron gun 11 is controlled so as to operate withinthe space charge limited condition by adjusting a current to be appliedto the graphite heater 112. Accordingly, this can reduce a shot noiseinduced by the electron beam to be significantly low. The electron beam,which has formed the crossover image C₁, is dispersed at a not-so-bigspreading angle and then focused by the condenser lens 17 so as to forma crossover image “C₂” in a location on a principal plane of theobjective lens 20. In this case, an excitation voltage of the condenserlens 17 is determined so that the electron beam can form the crossoverimage C₂ in the location on the principal plane of the objective lens20.

On the other hand, an image of the shaping aperture 13 formed by theelectron beam is demagnified by the condenser lens 17 into the image ina location “C₃”, and further demagnified by the objective lens into theimage of 0.1 μm or smaller on the surface of the sample S. Thisadjustment can be performed easily by changing the excitation voltage ofthe condenser lens 17.

For scanning the sample, the electrostatic deflector 18 and theelectrostatic deflector 191 of the E×B separator are used so as toprovide the scanning operation by way of a two-stage deflection. In thiscase, a total value of a deflection chromatic aberration, a comaaberration and an astigmatism may be minimized by setting a center ofdeflection in a location “C₄” directly above the objective lens 20.

The sample S is irradiated by the electron beam, and the secondaryelectrons emanated from the sample are accelerated and converged in anaccelerating electric field of the objective lens 20 and deflected bythe E×B separator 19 to be introduced into the secondary optical system30. In this case, normally, since a negative voltage has been applied tothe sample S by the power supply 22, almost all of the secondaryelectrons can pass through the objective lens 20 so as to be deflectedby the E×B separator 19. The secondary electrons are moved along theoptical axis B and detected by the detector 401.

It is to be noted that such an arrangement may be employed in which theaxisymmetric electrode 21 is disposed in the sample side with respect tothe objective lens 20, and a power supply 23 and its associated shiftswitch 24 for applying a positive or a negative voltage to thisaxisymmetric electrode 21 are provided, so that the axisymmetricelectrode 21 may be controlled to have a filtering function by applyingthereto a lower voltage than that of the sample. In such a case, apotential contrast of the pattern on the sample surface can be obtained.

Further, it may become possible to carry out defect inspection with highprecision by obtaining a normal image of the scanning electronmicroscope or by obtaining a potential contrast image through control ofthe shift switch 24 by using a computer. Consequently, the electron beamsystem according to the present invention is applicable to a defectinspection apparatus for a device.

An electron beam system 1′ according to a second embodiment of thepresent invention will now be described with reference to FIG. 2. Inthis drawing, the same components as those in the first embodiment shownin FIG. 1 are designated by the same reference numerals. Further,components corresponding to but different from components specified inthe first embodiment are designated by the same reference numerals anddenoted with a symbol “′”. The electron beam system 1′ according to thesecond embodiment, is different from that in the first embodiment, onlyin that it comprises a primary optical system 10′ and a detecting system40′. The primary optical system 10′ comprises an electron gun 11 havinga similar configuration to that in the first embodiment, anelectrostatic deflector 12 for axial alignment, a shaping aperture 13,an electrostatic deflector 14 for an axial alignment, a condenser lens17 for condensing an electron beam after it has passed through theshaping aperture 13, electrostatic deflectors 18, 25 for scanning, a NAaperture 16 and an objective lens 20, all of which are disposedappropriately with the electron gun 11 placed at a topmost location insuch a manner that an optical axis “A” of the electron beam emitted fromthe electron gun 11 may be normal to a surface “S” of a sample.

The electron gun 11 in this second embodiment can also be controlledwithin a space charge limited condition by adjusting a bias of a Wehneltelectrode to be deeper to some extent. As clearly shown in FIG. 2, theNA aperture 16 is disposed adjacent to the objective lens 20 in theelectron gun side with respect to the objective lens 20. Further,differently from the first embodiment, the axial aligning electrostaticdeflector is implemented as a two-stage configuration and no E×Bseparator nor axisymmetric electrode is provided. In the secondembodiment, a secondary optical system is not provided for its ownpurpose, but secondary electrons emanated from the sample S areattracted by an electric field of a detector 401′ of the detectingsystem 40′ to be introduced directly into the detector 401′, which willbe explained later. The detecting system 40′ comprises the detector401′, an A/D converter 402 and an image processing circuit 403.

An operation of the electron beam system having the configurationdesignated above according to the second embodiment will now bedescribed. An electron beam “C” emitted from the electron gun 11 passesthrough the shaping aperture 13 to form a crossover image “C₁” in apredetermined location between the shaping aperture 13 and the condenserlens 17, and then the beam is dispersed from the crossover image C₁′ ata spreading angle that is not too great. The dispersed electron beam isconverged by the condenser lens 17 to form a crossover image “C₂′” inthe NA aperture 16. After forming the crossover image C₂′, the electronbeam proceeds toward the sample S and is directed to the sample S by theobjective lens 20. An image of the shaping aperture 13 is demagnified bythe condenser lens 17 and the objective lens 20 into the image on thesample S. In order to scan the sample, the beam is deflected in atwo-stage manner by using the electrostatic deflector 18 and theelectrostatic deflector 25 for scanning.

The secondary electrons emanated from the sample S by the irradiation ofthe electron beam onto the sample S is deflected by the electric fieldof the deflector 401′ so as to be introduced into the deflector 401′.The deflector 401′ converts the detected secondary electron into anelectric signal indicative of intensity of the secondary electron. Theelectric signal output from the detector 401′ is converted by the A/Dconverter 402 into a digital signal and is then received by the imageprocessing circuit 403, where the digital signal is converted to imagedata. This image is compared to the reference pattern, and thereby anydefects in the sample S can be detected. Accordingly, the electron beamsystem of the second embodiment is also applicable to the defectinspection apparatus for a device.

The electron beam systems according to the first and the secondembodiments can be used to evaluate the sample after having beenfinished with those processes in a semiconductor device manufacturingmethod, which will be described later with reference to FIG. 7 and FIG.8. Applying the electron beam system of the present invention to atesting process in the manufacturing method for the semiconductor deviceenables such a semiconductor device having a fine pattern to beinspected with high throughput, thereby allowing for 100% inspection,thus improving an yield of the product and preventing the shipment ofany defective products.

Some further embodiments of the present invention will now be describedbelow with reference to FIG. 3 to FIG. 6. FIG. 3 shows one example ofconfiguration of an electron optical system in an electron beam systemaccording to a third embodiment of the present invention. In FIG. 3, anelectron gun 11 comprises a cathode 201 made of LaB₆ single crystal, aWehnelt 202 and an anode 203, which are operated within a space chargelimited condition. A primary electron beam emitted from the electron gun11 is converged by a first condenser lens 204 to form a crossover imagein a second aperture plate 205. A first aperture plate 206 has a squareopening and thereby enables a high beam current (an intensified primaryelectron beam) to be obtained. It is to be noted that if a slightlydeteriorated resolution in any specific direction is permissible, then arectangular opening, instead of the square opening, may be used. Thefirst aperture plate 206 having a shaping aperture is disposeddownstream to the first condenser lens 204, and a primary electron beamafter passing through the first aperture plate 206 is demagnified to be{fraction (1/100)} in scale with the aid of a second condenser lens 207and an objective lens 208 so as to form an image on a sample “S”, suchas a wafer. It is to be noted that reference symbol “SD1” designates afirst scanning deflector and “P” designates an optical axis of theoptical system.

In this third embodiment, the objective lens 208 may be, for example, anelectrostatic lens having three pieces of electrodes axisymmetric withrespect to the optical axis P. One among three electrodes, which isdisposed in the electron gun side, is controlled to have a voltageproximal to the ground, which will be changed to provide dynamicfocusing, thereby correcting an image field curvature aberration or afluctuation in height of the sample surface during a movement of astage. A central electrode is applied with a positive high voltage, andthis can enhance a focusing action for the primary electron beam andreduce an axial chromatic aberration. On the other hand, a secondaryelectron beam emanated from the sample S is accelerated by theacceleration field produced by the electrodes of the objective lens 208,and all of the secondary electrons pass through the objective lens 208when a topographical image or a material image of the sample surface isto be formed. That is, at least two electrodes are adapted to havedesired voltages applied thereto. Ideally, three of the electrodes maybe preferably controlled to have desired voltages, respectively.Employing such axisymmetric electrodes would not produce anon-axisymmetric electric field, thereby preventing any additionalaberration from being generated.

An E×B separator 210 is disposed upstream to the objective lens 208, andthis E×B separator 210 deflects the secondary electron beam off from theoptical axis of the primary optical system (to deflect it toward theright hand direction on the paper in FIG. 3). The deflected secondaryelectron beam passes through a shielded pipe 211 and then it is detectedby a secondary electron detector 212.

Measuring a noise contained in a signal detected by the secondaryelectron detector 212 makes it possible to determine whether or not theelectron gun 11 made of Lab₆ single crystal is operating in the spacecharge limited condition. That is, assuming the shot noise is denoted by“N” and expressed in the following equation:N²=Γ²eI_(e)Δf,if the “Γ” is smaller than 1, it is determined that the electron gun 11is operating in the space charge limited condition. Wherein, the “Γ” isa shot noise reduction coefficient, the “e” represents a charge of anelectron, the “I_(e)” represents a current detected by the secondaryelectron detector 212, and the “Δf” represents a band width in which thenoise is measured. It is to be noted that preferably the Γ is equal toor less than 0.5, ideally equal to or less than 0.2.

In contrast to that the Γ=1 in the electron gun of schottky cathodetype, since the present invention employs an electron gun operating in aspace charge limited condition, a shot noise can be reduced by Γ timesand thus a beam current Γ² times high as that attainable by the priorart can be made available to obtain a signal with a desired S/N ratio,or a signal having the same S/N ratio can be obtained in a measuringtime multiplied by Γ².

In a fourth embodiment of the present invention, defect inspection iscarried out by using the electron beam system comprising the electronoptical system shown in FIG. 3, in which, for example, a electricresistance of a via connection with a lower-layer wiring may beevaluated, said via being used to connect the lower-layer wiring and anupper-layer wiring in a multi-layered wiring sample. Evaluating theelectric resistance of the via connection with the lower-layer wiringtakes advantage of such a characteristic that when the charge is givento the surface of the sample, if the lower-layer wiring is grounded oralmost grounded and the electric resistance between the via connectionand the lower-layer wiring is sufficiently small, then the via mayimmediately return back to the ground potential, but if the electricresistance between the via connection and the lower-layer wiring isgreat, then the via may be charged to positive. Accordingly, measuringthe surface potential immediately after the injection of the charges tothe sample by the electron beam system shown in FIG. 3 allows theelectric resistance of the via connection with the lower-layer wiring tobe evaluated. Further, measuring the changes in potential of the viaover time can provide a more accurate measurement of the electricconnection resistance, and also using the electron beam system of FIG. 3to perform the defect inspection can improve the throughput.

Normally, the via has a cross sectional area as small as the minimumline width at a location along the surface of the lowest layer of themulti-layered wiring, and the cross sectional area thereof becomesgradually bigger toward the topmost layer. When the via has a greatersectional area, it may be better to use a greater diameter of the beamso that the defect inspection can be carried out at high rate.Accordingly, in the fourth embodiment, when the via having the largerdiameter is to be evaluated, the position of the second aperture plate205 of FIG. 3 along the optical axis may be changed and also thedemagnified ratio of the beam from the first aperture plate 206 may bechanged, thereby obtaining the beam having a desired diameter. Further,upon making the probe beam by forming a crossover enlarged image ordemagnified image on the sample surface, the crossover reducing ratioshould be changed.

Turning now to FIG. 4, how to apply the defect inspection to the via byusing the electron beam system shown in FIG. 3 will now be described. Afield of view for scanning by the electron beam system is indicated by arectangular shape 3-1 of dotted line. The area within this field of viewfor scanning 3-1 is raster scanned along the solid line 3—3 by theelectron beam system. The secondary electrons generated by this rasterscanning are detected by the secondary electron detector 212 to obtainthe SEM image. Since the secondary electron emission efficiency ishigher in the location including a via 3-2 within the field of view forscanning 3-1, a brighter image can be acquired therein, which is thenstored. This means that a different image would be obtained independence on the variation in the material of the sample surface. Whenthe SEM image is to be obtained, since the ground voltage is beingapplied to the one electrode most proximal to the sample among thoseelectrodes of the objective lens while the negative voltage is beingapplied to the sample S, therefore the secondary electrons areaccelerated so as to be efficiently detected.

A fifth embodiment of the present invention relates to a technology formeasuring a potential contrast by using the electron beam system shownin FIG. 3. FIG. 5 is a diagram illustrating specifically a physicalrelationship between the objective lens 208 of FIG. 3 and the sample S.It is to be noted that FIG. 5 shows only a left half of a cross sectionincluding the optical axis P of three electrodes of the objective lens208, an upper electrode 8-1, a central electrode 8-2, and a lowerelectrode 8-3, as well as the sample S, so that a 3D figure formed byturning the cross section of the electrodes around the optical axis Pshows an actual unit of electrodes. Reference numeral 8-4 designatesinsulating spacer for insulating the upper electrode 8-1, the centralelectrode 8-2 and the lower electrode 8-3 from each other. The thicknessof each insulating spacer and the interval between the insulatingspacers are both 2 mm, for example. If a voltage lower than that of thesample S is applied to this lower electrode 8-3 of the objective lens 8,the potential contrast for the pattern formed on the sample S can bemeasured. This will be described with reference to FIG. 6.

FIG. 6 shows a result of a simulation which shows that a potentialcontrast can be measured by this electron beam system, in which avoltage lower than that of the sample S by 300V is applied to the lowerelectrode 8-3 most proximal to the sample among the electrodes of theobjective lens 208. In FIG. 6, reference numeral 221 designates anequipotential surface of −1V, reference numeral 222 designates antrajectory of the secondary electron emitted from the pattern having apotential of 2V at an initial speed of 0.2 eV, and reference numeral 223designates an trajectories of the secondary electron emitted from thepattern having a potential of 0V at an initial speed of 0.2 eV.

Is can been seen from FIG. 6 that the secondary electrons emitted fromthe pattern having the potential of 2V are returned back to the sample Sside, but the secondary electrons emitted from the pattern having thepotential of 0V passed through those three electrodes, the upperelectrode 8-1, the central electrode 8-2 and the lower electrode 8-3.This indicates that those secondary electrons from the pattern havingthe potential of 0V can be detected, but those secondary electrons fromthe pattern having the potential of 2V cannot be detected, which meansthat the potential contrast can be measured.

A sixth embodiment of the present invention will now be described. Whenthe potential contrast is to be measured, since the voltage lower thanthat of the sample S by approximately 300V is applied to the electrodemost proximal to the sample S among those electrodes of the objectivelens 208, the potential contrast can be obtained, but instead, anaberration characteristic of the objective lens 208 may be deteriorated,and if the beam is converged, then the beam current is apt to be smallerand thereby the S/N ratio may also become lower. As one solution to thisproblem, scanning may be skipped for the locations containing no viaduring measuring the potential contrast, as shown in 3-4. That is, onlythe locations containing vias should be selectively scanned. If thesystem is controlled to apply the irradiation only to the vias, then themeasuring time would be further shortened. Besides, preferably, thegeometry of the beam may be shorter in the scanning direction but may belonger in the direction normal to said scanning direction, as shown by235 in FIG. 4. This ensures that the via may be scanned properly, evenin the case of the slightly offset operational position. Such geometryof the beam may be formed through the aperture provided in the firstaperture plate 205 of FIG. 3.

According to a seventh embodiment of the present invention, when avoltage applied to the electrode most proximal to the sample 8 amongthose electrodes of the objective lens 208, i.e., the lower electrode8-3, is changed, depending on a case where the raster scan is carriedout to obtain the SEM image or a case where the potential contrast ismeasured, the voltage applied to the central electrode representing thefocusing condition in the sample S may be also changed.

It is to be appreciated that scanning for the purpose of giving chargesto the sample S by the electron beam system shown in FIG. 3 may becarried out with an optimal landing energy, that is, a landing energythat can provide a desired potential with a least dose. Adjusting thislanding energy can be performed by changing a cathode potential of theelectron gun 11 and/or changing a retarding voltage to be applied to thesample S.

Turning now to flowcharts in FIG. 7 and FIG. 8, a semiconductor devicemanufacturing method by using the electron beam system of the presentinvention will be described. The electron beam system of the presentinvention may be used to evaluate a wafer in the course of processing orafter having been processed in the flowcharts of FIG. 7 and FIG. 8.

As shown in FIG. 7, the semiconductor device manufacturing method, ifgenerally segmented, may comprise a wafer manufacturing process S1 formanufacturing a wafer, a wafer processing process S2 for providing anyprocessing required for the wafer, a mask manufacturing process S3 formanufacturing the mask required for exposure, a chip assembling processS4 for cutting out those chips formed on the wafer one by one so as tomake them operative, and a chip testing process S5 for testing thefinished chips. Each of those processes includes some sub steps,respectively.

Among the processes described above, the process which may givecritically effect semiconductor device manufacturing is the waferprocessing process. The reason is that in this process, a designedcircuit pattern is formed on the wafer and also a lot of chips areexpected to operate as a memory, or a MPU are formed thereon.

Thus, it is important to evaluate the processed condition of the waferrepresenting the result of the processes executed in the sub steps ofthe wafer processing process which has much effect on the manufacturingof the semiconductor wafer, and those sub steps will be described below.

First of all, a dielectric thin film for functioning as an insulationlayer is deposited, and a metal thin film is also deposited, which formsa wiring section and an electrode section. The film deposition may beperformed by the CVD or the sputtering. Then, the deposited dielectricthin film and metal thin film together with the wafer substrate areoxidized, and also a resist pattern is formed in a lithography processby using a mask or reticle produced in the mask manufacturing processS3. Then, the substrate is processed according to the resist pattern byusing the dry etching technology or the like, and ions or otherimpurities are implanted therein. After that step, the resist layer isremoved, and the wafer is subjected to testing.

Such a wafer processing process as described above may be repeated by adesired number of layers to produce the wafer which in turn is separatedinto respective chips in the chip assembling process S4.

FIG. 8 is a flow chart illustrating the lithography process included asa sub step in the wafer processing process of FIG. 7. As shown in FIG.7, the lithography process includes a resist coating step S21, anexposing step S22, a developing step S23 and an annealing step S24.

In the resist coating step S21, the resist is applied onto the wafer, onwhich the circuit patter has been formed by using the CVD or thesputtering, and then in the exposing step S22, the applied resist isexposed. Then, in the developing step S23, the exposed resist isdeveloped so as to obtain the resist pattern, and in the annealing stepS24, the developed resist pattern is annealed to be made stable. Thosesteps S21 to S24 may be repeated by a desired number of layers.

According to the semiconductor device manufacturing method of thepresent invention, since the electron beam system as discussed withreference,to FIG. 3 to FIG. 6 is used in the chip testing process S5 fortesting the finished chips, therefore even in the case of thesemiconductor device having a fine pattern, an image with a reduceddistortion and/or out-of-focus can be obtained and thereby any defectsin the wafer can be detected with high reliability.

FIG. 11 shows an electron beam system (an electron optical system) 600to which the present invention can be applied. In FIG. 11, an electronbeam emitted from a cathode 601a contained in an electron gun 601 isfocused by a condenser lens 603 into a crossover image at a point 605. Afirst multi-aperture plate 607 having a plurality of apertures isdisposed below the condenser lens 603, and with the aid of this, aplurality of primary electron beams is formed respectively. Each of theprimary electron beams formed by the first multi-aperture plate 607 isdemagnified by a demagnifying lens 609 so as to be projected onto apoint 611. That beam is, after having been focused on the point 611,further focused by an objective lens 613 onto a sample S. The pluralityof primary electron beams exiting from the first multi-aperture plate607 is deflected so as to synchronously scan a surface of the sample Sby a deflector 617 disposed between the demagnifying lens 609 and anobjective lens 613.

In order to eliminate an image field curvature aberration of thedemagnifying lens 609 and the objective lens 613, a plurality of smallapertures are arranged along a circle on the multi-aperture plate 607 insuch a manner that the projections of respective apertures in theY-direction may be equally spaced. The electron gun 601, the condenserlens 603, the first multi-aperture plate 607, the deflector 617 and theobjective lens 613 all together make up a primary optical system 536having an optical axis 535.

A plurality of points on the sample S is irradiated by the thus focusedplurality of primary electron beams respectively, and secondary electronbeams emanated from said plurality of points are attracted by theelectric field of the objective lens 613 to be converged narrower andthen deflected by an E×B separator 619 to be introduced into a detectingsystem 538. Those secondary electron beams are focused at a point 621closer to the objective lens 613 as compared with the point 611. This isbecause each of the primary electron beams has an energy of 500 eV onthe sample surface, while in contrast, each of the secondary electronbeams has only an energy of a few eV.

The detecting system 538 has magnifying lenses 623, 625, and thesecondary electron beam after passing through those magnifying lenses623, 625 passes through a plurality of apertures 627 a of a secondmulti-aperture plate 627 and then is formed into images on a pluralityof detectors 629. It is to be noted that each of the plurality ofapertures 627 a formed in the second multi-aperture plate 627 disposedin front of the plurality of detectors 629 corresponds respectively toeach of a plurality of apertures 607 a formed in the firstmulti-aperture plate 607 on the one-to-one basis.

Each of the detectors 629 converts the detected secondary electron beaminto an electric signal indicative of its intensity. The electricsignals output from respective detectors are amplified by the amplifier631 and received by the image processing section 633, respectively,where the signals are converted into image data. Since the imageprocessing section 633 is further provided with a scanning signal whichhas been used for deflecting the primary electron beam, the imageprocessing section 633 can display an image representing the surface ofthe sample S. A defect in the surface of the sample S can be detected bycomparing the image with a reference pattern, and also a line width ofthe pattern on the sample S can be measured by moving the sample S intothe vicinity of the optical axis of the primary optical system 536through the registration and then extracting a line width evaluationsignal through a line scanning, which is then appropriately calibrated.

At this point, a special care must be taken in order to minimize aneffect from three kinds of aberrations, i.e., the distortion induced inthe primary optical system, the image field curvature aberration and theastigmatism when the primary electron beam after passing through theapertures of the first multi-aperture plate 607 is formed into an imageon the surface of the sample S and the secondary electron beam emanatedfrom the sample S is formed into an image on the detector 629.

Then, as to the relationship between a distance among a plurality ofprimary electron beams and the detecting system 538, if the primaryelectron beams are arranged to be spaced from each other by a distancegreater than the aberration of the detecting system 538, cross talkamong the plurality of electron beams can be eliminated. It is to benoted that in FIG. 11, reference numeral 626 illustrates trajectory ofspecific secondary electrons among those secondary electrons emanatedfrom the irradiation points of the primary electron beam on a circle,which have been emanated from two points on a diameter of the circle inthe directions normal to the sample surface. An aperture 628 is arrangedin a location where those trajectories cross the optical axis 539, suchthat the aberration in the value converted into that on the samplesurface may be made smaller than the minimum value of the beam-to-beamdistance of the primary electron beams. Further, in FIG. 11, referencenumeral 618 designates an axisymmetric electrode for measuring thepotential of the pattern on the wafer.

As for the control of the dose, during fly-back of the scanningoperation the multi-beam is deflected by a deflector 635 so as to beblocked by a knife edge 637 for blanking, while at the same time, thecurrent absorbed into this knife edge is measured by an am meter 639,and the dose per unit area is calculated by a dose calculating circuit641. The thus calculated value is stored in a storage 645 through a CPU643.

Further, if the dose per unit area exceeds a predetermined value, theCPU 643 may invoke an electron gun control power supply 647 to decreasethe voltage to be applied to a Wehnelt electrode 601 b, thereby reducingthe beam current to decrease the dose. Further, when the control is notable to catch up with the increase of the dose and ultimately the doseper unit area ends at a level higher than, for example, 3 μc/cm², thenthe data of the corresponding irradiation area is just output by anoutput means 649, and the evaluation is carried on.

FIG. 12 shows an electron beam system (mainly a movable stage) 70 towhich the present invention can be applied. In this embodiment, a term“vacuum” means a vacuum typically referred to in this technical field.In the electron beam system 70 of FIG. 12, a tip end portion of aoptical column 71 for irradiating an electron beam against a sample,i.e., an electron beam irradiation section 72, is installed in a housing84 defining a vacuum chamber “C”. Right below the optical column 71 isprovided an XY stage 73 of high precision, in which an X table 74movable in the X direction (the left and right direction in FIG. 12) ismounted on a Y-directionally (the direction vertical to the paper inFIG. 12) movable table 75. The sample S is loaded on the X table 74. Thesample S is positioned correctly with respect to the optical column 71by the XY stage 73, so that an electron beam from the optical column 71may be irradiated onto a predetermined point on a surface of the sample.

A pedestal 76 of the XY stage 73 is fixed to a bottom wall of thehousing 84, and the Y table 75 movable in the Y direction (the verticaldirection with respect to the paper in FIG. 12) is mounted on thepedestal 76. On both side faces of the Y table 75 (a left and a rightside faces in FIG. 12), protrusions are formed, which are protruded intoconcave recesses formed in a pair of Y-directional guides 77 a and 77 bin their side surfaces facing to the Y table respectively. Each of theconcave recesses extends in the Y direction along almost the full lengthof each of the Y-directional guides.

Hydrostatic bearings 81 a, 79 a, 81 b, 79 b having a known structure areprovided respectively in an upper and a lower faces and side faces ofthe protrusions protruding into the concave recesses, and a highpressure gas is blown out via those hydrostatic bearings, so that the Ytable 75 can be supported in a non-contact manner with respect to theY-directional guides 77 a, 77 b and thereby allowed to make areciprocating motion in the Y direction smoothly. Further, a linearmotor 82 having a known structure is disposed between the pedestal 76and the Y table 75 and a Y directional driving is performed by thelinear motor 82. A high pressure gas is supplied to the Y table 75through a flexible pipe 92 for feeding the high pressure gas, andfurther distributed to the hydrostatic bearings 79 a to 81 a and 79 b to81 b through a gas passage (not shown) formed within the Y table. Thehigh pressure gas supplied to the hydrostatic bearings is blown out intoa gap in a range of some microns to some ten microns formed between theY table and a oppositely positioned guide plane of each of the Ydirectional guides, and herein the high pressure gas has a role inpositioning the Y table 75 accurately with respect to the guide planesin the X direction and the Z direction (in the up and down direction inFIG. 12).

The X table 74 is operatively mounted on the Y table 75 so as to bemovable in the X direction (the left and right direction in FIG. 12). Apair of X directional guides 78 a, 78 b (only 78 a is shown) having thesame structure as that of the Y directional guides 77 a, 77 b isdisposed on the Y table 75 with the X table 74 interposed therebetween.A concave recess is also formed in each of the X directional guides intheir side surfaces facing to the X table 74. Each of the concaverecesses extends along almost full length of each of the X directionalguides. Hydrostatic bearings (not shown) similar to said hydrostaticbearings 81 a, 79 a, 80 a, 81 b, 79 b, 80 b are arranged in a similarorientation in upper and a lower faces and side faces of each protrusionof the X directional table 74 protruding into the concave recess. Alinear motor 83 having a known structure is disposed between the Y table75 and the X table 74, and the X directional driving of the X table isperformed by that linear motor 83.

A high pressure gas is supplied to the X table 74 through a flexiblepipe 91 and further distributed to the hydrostatic bearings. This highpressure gas is blown out against the guide plane of the X directionalguide from the hydrostatic bearings, and thereby the X table 74 can besupported with high precision with respect to the Y directional guide inthe non-contact manner. A vacuum chamber “C” is evacuated by a vacuumpump or the like having a known structure through vacuum pipes 89, 90 a,90 b connected thereto. Inlet sides of the pipes 90 a, 90 b (inside ofthe vacuum chamber) are extended through the pedestal 76 and open in theupper surface thereof in the vicinity of a location where the highpressure gas is discharged from the XY stage 73, so that the increase inthe pressure in the vacuum chamber may be prevented as much as possible,which may otherwise be caused by the high pressure gas blown out fromthe hydrostatic bearings.

A differential exhaust mechanism 95 is arranged in the surrounding ofthe electron beam irradiation section 72 or the tip end of the opticalcolumn 71 so as to keep the pressure within the electron beamirradiation space 87 to be sufficiently low even if the pressure withinthe vacuum chamber C is high. That is, an annular member 96 of thedifferential exhaust mechanism 95 mounted to the periphery of theelectron beam irradiation section 72 is positioned with respect to thehousing 94 such that a minute gap 110 (in a range of some microns tosome ten microns) may be created between the lower surface of theannular member 96 (the surface facing to the sample S) and the sample S,and an annular groove 97 is formed in the under surface of the annularmember 96.

The annular groove 97 is connected to a vacuum pump, though not shown,via an exhaust pipe 98. Accordingly, the minute gap 110 may be evacuatedthrough the annular groove 97 and the exhaust port 98, so that any gasmolecules trying to enter the electron beam irradiation space 87surrounded by the annular member 96 from the vacuum chamber C can beexhausted. By way of this, the pressure within the electron beamirradiation space 87 can be kept to be low, and thereby the electronbeam can be irradiated without causing any problem. This annular groovemay employ a double or a triple structure depending on the pressurewithin the chamber and/or the pressure within the electron beamirradiation space 87.

As the high pressure gas to be supplied to the hydrostatic bearings,typically dry nitrogen gas may be employed. However, if possible,preferably an inert gas of higher purity should be used. This is becauseif any impurities, such as water content or oil content, are containedin the gas, those impurities may adhere to the inner surface of thehousing defining the vacuum chamber or to the surfaces of the stagecomponents, which in turn deteriorate the vacuum level, or otherwisethey may adhere to the surface of the sample, which also in turnreversely affect the vacuum level in the electron beam irradiationspace. Typically, the sample S is not directly loaded on the X table,but may be loaded on a sample table having functions for detachablyholding the sample and/or for applying a minor position change withrespect to the XY stage 73.

Since the stage mechanism of the hydrostatic bearing used in theatmosphere may be employed in the electron beam system 70 almost withoutany modification, an XY stage having as high precision as the stagespecified for the atmosphere used in the exposing apparatus can beachieved for the XY stage specified for the electron beam system withapproximately the same cost and size. The structure and configurationfor the hydrostatic guide and the actuator (linear motor) as describedabove have been given by way of example only, but any hydrostatic guideand actuator usable in the atmosphere can be employed.

FIG. 9 is a general schematic diagram illustrating an arrangement of anelectrostatic capacity sensor in an electron beam system according to anembodiment of the present invention. In the electron beam system, fourelectrostatic capacity sensors 502 a, 502 b, 502 c and 505 are disposedalong a periphery 503 of a disc shaped 12 inch wafer 1 to be loaded onthe movable stage, which is not shown. Three of the sensors 502 a, 502 band 502 c are arranged so as to be equally spaced from each other, whilethe sensor 505 is provided to adjust a rotational orientation of thewafer and is disposed in a location between the sensor 502 b and thesensor 502 c where a notch 504 or an orientation flat should be normallylocated. Herein, the notch or the orientation flat is provided bycutting out a portion of the contour of the disc-like wafer in order tospecify the direction of rotation of the wafer. The notch is defined asa V-shaped cut-out, while the orientation flat is a linear cut-outnormal to a radial direction of the wafer. A position of each of theelectrostatic capacity sensors 502 a, 502 b, 502 c and 505 with respectto the wafer on the movable stage may be determined such that the wafermay overlap approximately a half of each electrode. A distance (dx, dy)between an optical axis (0, 0) of the electron optical system and thecenter of gravity of three electrostatic capacity sensors 502 a, 502 band 502 c is measured in advance.

Positioning of the wafer loaded on the electron beam system may becarried out in the following manner. The disc-like wafer S mounted onthe movable stage is brought by the movement of the movable stage into aposition where the periphery 503 of the wafer comes into engagement withrespective electrostatic capacity sensors 502 a, 502 b, 502 c and 505,as shown in FIG. 9. At first, the electrostatic capacity is measured bythree of the sensors 502 a, 502 b and 502 c which have been disposed tobe spaced equally from each other, and the measured values from thosethree sensors 502 a, 502 b and 502 c are compared to one another, andthen the xy position of the wafer is adjusted by the movable stage suchthat those three sensors may indicate the same measured values.

In the case where the wafer is in a location offset to the right handside in FIG. 9, since the measured value from the sensor 502 c may begreater, while the measured value from the sensor 502 b may be smaller,therefore the wafer is shifted to the left hand side so as to make bothmeasured values equal. If the measured value from the sensor 502 a issmaller than the measured value from the sensor 502 b, the wafer shouldbe shifted upwardly, and if greater, then the wafer should be shifteddownwardly to make the measured values equal to each other. In this way,the center position (the center of gravity position G) of the wafer canbe made to match the center of gravity position for the three sensors502 a, 502 b and 502 c, or the optical axis position (0, 0) of theelectron optical system. After this, in order to correct the rotationalorientation of the wafer, a θ table is moved to minimize the measuredvalue from the electrostatic capacity sensor 505.

In the above embodiment, the four electrostatic capacity sensors 502 a,502 b, 502 c and 505 are used to position the wafer relative to themovable stage with a position accuracy of ±20 μm and a rotation accuracyof ±10 mrad. By moving the movable stage by the distance (dx, dy), thecenter of the wafer can be brought into a position right below theelectron optical system or the optical axis position (0, 0) thereof soas to match therewith with the position accuracy of ±20 μm.

When the field of view of the electron optical system is defined by adiameter of 200 μm, a corner portion (an edge) created by 100 μm widedicing lines can be obtained in an SEM image. The dicing line is definedas a region containing no device pattern arranged between dies and ithas a width slightly greater than the thickness of a saw blade used forcutting out dies from the wafer so as to separate one die from anotherdie in the X direction and the Y direction. It can be accuratelymeasured from the SEM image how much the center position of the wafer isoffset from that of the electron optical system. Therefore, uponperforming defect inspection of the pattern, this offset is compensatedfor on the basis of the SEM image and then the comparison is maderelative to the reference pattern, thereby making it possible to detectthe defect.

Discussing now a problem that the rotational orientation of the wafermay fall only within a range of ±10 mrad, any offset of the rotationalorientation can be accurately measured by moving the movable stage intoa position where the optical axis of the electron optical system comesinto match with the dicing line in the periphery of the wafer, takingthe SEM image in that position and then comparing it to that taken inthe center to determine the offset therebetween. The correction may beperformed with the θ table, or alternatively the stage may be run alongthe orientation of the pattern on the wafer during the continuousdriving of the stage.

A method for evaluating an image, in which alignment has not beenaccomplished correctly, by using a pattern matching will be describedwith reference to FIG. 10. FIG. 10 a is an SEM image including a fieldof view 521 obtained by the electron optical system, while FIG. 10 b isa reference image including a field of view 522. By comparing respectivepattern corner portions 525, 526, 527, 528 in the vicinity of fourcorners of the field of view 521 of the SEM image with respectivepattern corner portions 525′, 526′, 527′, 528′ in the vicinity of fourcorners of the reference image including the field of view 522 to oneanother, respectively, those offsets in position, rotation andmagnification of the SEM image from the reference image can becalculated.

The reason why four points are selected in each image is to allow apattern matching to be conducted correctly, even if the defects residein the pattern corner portions to be compared. As shown in FIG. 10 a, ifa defect 529 happens to reside in the vicinity of the pattern cornerportion 252, a magnification compared in 525-527, or (a distance between525 and 527)/(a distance between 525′ and 527′), may be different from amagnification compared in 526-528, or (a distance between 526-528)/(adistance between 526′ and 528′), which indicates that there must be adefect in some pattern. In this case, if further a magnificationmeasured in 525-528 is compared to a magnification measured in 526-527,the result would be, for example,(525-527)/(525′-527′)=1.01(526-528)/(526′-528′)=1.05(526-527)/(526′-527′)=1.05(525-528)/(525′-528′)=0.99which indicates that the pattern corner 525 must contain the defect. Itis a matter of course that the rotation angle may be compared.

FIG. 10 c shows a case of a pattern corner shaped into arc 531. In thiscase, an accurate evaluation of a pattern can be obtained by consideringan intersection 526 of extensions of two sides to be a pattern corner.

An electron beam system according to the present invention shown in FIG.11 may be applicable to a semiconductor device manufacturing methodshown in FIG. 7 and FIG. 8. That is, the electron beam system of FIG. 11is applicable to the process for evaluating a processed condition of awafer (wafer testing) in the wafer processing process, and if applied tothe chip testing process for inspecting the finished chip, then a defectin a wafer can be detected with high accuracy.

FIG. 13 a and FIG. 13 b are diagrams for illustrating a position sensor540 of electrostatic capacity type, wherein FIG. 13 a is a plan viewshowing a physical relationship between an electrode of the positionsensor and a wafer, while FIG. 13 b contains a side elevational viewshowing a physical relationship between the electrode of the positionsensor and the wafer as well as a block diagram of other maincomponents. As shown in FIG. 13 a and FIG. 13 b, an electrode 541 of theposition sensor 540 has an elongated plate-like shape and it ispositioned in parallel with the surface of the wafer S as spaced fromthe surface by a predetermined distance “H”. The wafer S and theelectrode 541 are electrically connected to an electrostatic capacitymeasuring instrument 546, and an electrostatic capacity “Q” betweenthese two components is measured. The electrostatic capacity measuringinstrument 546 may be a commercially available impedance measuringinstrument.

The electrostatic capacity Q between the wafer S and the electrode 541is proportional to an overlapped area 542 of the wafer S with respect tothe electrode 541. As shown in FIG. 13 a, assuming that the shape of theelectrode 541 is a rectangle and the electrode 541 is disposed in theradial direction of the wafer, then the area of the overlapped portion542 may be proportional to a length “x” of the overlapped portion of theelectrode 541 with respect to the wafer S in the radial directionthereof. Accordingly, by preparing a comparison table 547 containing arelationship between the length “x” and the electrostatic capacity Q,which has been determined in advance, the overlapped portion length “x”,or the position of the wafer S, can be determined on the basis of thecomparison table and the measured electrostatic capacity Q. As shown inFIG. 13 b, the measured electrostatic capacity Q and the data from thecomparison table 547 are input into the position detector 548, which inturn outputs the wafer position data.

EFFECTS OF THE INVENTION

According to the present invention, the following effects may be broughtabout.

(1) As compared with an optical system using a three-stage of lensesaccording to the prior art, in the present invention, a number of stagesof lenses can be reduced to two, and accordingly a lens axis aligningdevice may be made one stage less. Consequently, a length of an opticalpath may be made shorter and out-of-focus of an electron beam due to aspace charge effect may be reduced. Further in the present invention,since a number of parts to be used in the optical system and a controlcircuit can be reduced by a number corresponding to one-stage of lensand one-stage of electrostatic deflector, therefore a reliability of theelectron beam system can be improved.

(2) As compared to a crossover image demagnification type beam, in thepresent invention, a higher beam current can be obtained by using thesame electron beam size.

(3) Since the electron gun can be operated in the space charge limitedcondition, a shot noise in the electron beam can be significantlyreduced, and thereby a noise in the secondary electrons signal can bereduced.

(4) Since a NA aperture is disposed in a front location with respect toa demagnification lens, a detector of the secondary electrons can bedisposed in a front location with respect to an objective lens.

(5) When the NA aperture is disposed adjacent to the objective lens, itis no more necessary to accurately position a crossover image point ofthe electron beam.

(6) Since the electron gun is used in the space charge limitedcondition, a signal having a greater S/N ratio can be obtained by usingthe same level of beam current as compared to the case of using anelectron gun of the schottky cathode type. In this case, preferably ashot noise reduction coefficient is 0.5 or lower, and more preferably0.2 or lower.

(7) Since the secondary electrons generated from a pattern of highvoltage can be returned back toward the sample by applying a voltagelower than that of the sample to an electrode most proximal to thesample among the electrodes of the objective lens, therefore not onlythe potential contrast can be measured but also upon obtaining an SEMimage, the secondary electrons can be detected with high efficiency bygrounding this electrode.

(8) Upon measuring the potential of the sample, an inspection can befinished within a shorter time as compared to a full surface scanning byapplying an irradiation selectively only to a location containing a via.

(9) Since an optimal operating condition, for example, a beam diameter,can be set selectively in each individual case for obtaining the SEMimage, for giving charges to the sample, or for measuring a potentialcontrast, therefore an inspection with high precision can be achievedwith high throughput.

(10) Since a defect inspection can be carried out with high throughput,therefore a device can be manufactured with high yield.

(11) An inspection apparatus of the present invention can provide aninnovative electron beam system, in which an inspection of a wafer canbe performed without destroying a gate oxide or the like by performingan alignment operation without using any electron beam.

(12) According to the present invention, since an optical microscope foralignment operation is not required to be installed in a vacuumenvironment, an electron beam system may have a more simplifiedstructure and thereby can be manufactured at lower price. Further, therewould be no more alignment time, and so a throughput (a processingvolume per time) can be improved.

(13) According to the present invention, a pattern matching is conductedby using four or more points, so that no error may be produced even if adefect resides at a point to be evaluated, and also a pattern matchingcan be performed correctly even if a corner portion of the pattern has acurvature.

1. An electron beam system which comprises a primary optical system forirradiating an electron beam emitted from an electron gun onto a sampleand detects secondary electrons emanated from a surface of the sample,wherein a shaping aperture is disposed in a front location of saidelectron gun, wherein an image of the shaping aperture by irradiation ofthe electron beam from said electron gun is demagnified and formed onthe sample surface, wherein said electron gun is a thermionic emissionelectron gun and a shaping aperture and a NA aperture are disposed infront locations of said thermionic emission electron gun, and whereinsaid image of the shaping aperture is demagnified and formed on thesample surface by using lenses having at least two steps.
 2. An electronbeam system according to claim 1, in which the shaping aperture and atwo-step lenses are arranged in said primary optical system and an E×Bseparator is arranged between said two-step lenses, wherein the image ofthe shaping aperture by irradiation of the electron beam from saidelectron gun is demagnified and formed on the sample surface by saidtwo-step lenses and secondary electrons emanated from the sample surfaceare separated by said E×B separator from the primary optical system andintroduced into a detector.
 3. An electron beam system according toclaim 1, wherein in said primary optical system, the shaping aperture, aNA aperture, and a lens are disposed in sequence along an optical axisof the primary optical system, and a crossover image of the electronbeam from said electron gun is focused to said NA aperture bycontrolling a an electrode potential bias of said electron gun.
 4. Anelectron beam system according to claim 1, in said primary opticalsystem, the shaping aperture and a lens are disposed in sequence alongan optical axis of the primary optical system, and a NA aperture isdisposed in a location adjacent to said lens in the electron gun sidewith respect to said lens, wherein a crossover image of the electronbeam is formed in said NA aperture.
 5. An electron beam system accordingto claim 1, wherein the electron beam system is a defect inspectionapparatus.
 6. A device manufacturing method comprising the steps of: a.providing a wafer; b. processing the wafer; c. detecting a defect on aprocessed wafer using the electron beam system of claim 1; d. repeatingnecessary times of the steps b and c; e. assembling the wafer into adevice.
 7. An electron beam system which comprises a primary opticalsystem for irradiating an electron beam emitted from an electron gunonto a sample and detects secondary electrons emanated from a surface ofthe sample. wherein a shaping aperture is disposed in a front locationof said electron gun, wherein an image of the shaping aperture byirradiation of the electron beam from said electron gun is demagnifiedand formed on the sample surface, wherein said electron gun is athermionic emission electron gun and a shaping aperture and a NAaperture are disposed in front locations of said thermionic emissionelectron gun in sequence, and wherein a crossover image formed by anelectron beam from said thermionic electron gun is enlarged and formedinto an image in said NA aperture.
 8. An electron beam system in which aprimary electron beam emitted from an electron gun is irradiated onto asample surface and then a secondary electron beam emanated from saidsample is detected, said system characterized in further comprising anobjective lens for focusing said primary electron beam as well asaccelerating said secondary electron beam, wherein said objective lenshas a function of scanning all field of view and function of selectivelyscanning a specific pattern.
 9. An electron beam system according toclaim 8, wherein said electron gun is operated in a space charge limitedzone, meaning that a shot noise reduction coefficient is smaller than 1,and a voltage to be applied to an electrode most proximal to said sampleamong electrodes of the objective lens can be set to a desired value.10. An electron beam system according to claim 8, wherein a beam size ofsaid electron beam can be changed between a case for irradiating saidelectron beam against said sample thus to form a topographical image ora material image of the sample surface and another case for measuring apotential of a pattern formed on said sample.
 11. A defect inspectionmethod by using an electron beam system as defined in claim 8,comprising: an image acquiring step for irradiating an electron beamemitted from said electron gun against said sample via said objectivelens thus to obtain an image of a sample surface; a measuring step formeasuring a potential or a variation thereof on the surface of saidsample, which has been induced by said irradiation of the electron beam;and a determining step for determining whether a specific pattern isgood or bad based on said potential or said variation thereof; whereinin said image acquiring step and said measuring step, a voltage to beapplied to an electrode most proximal to said sample among electrodes ofsaid objective lens can be changed.
 12. A method for manufacturingdevices comprising the steps of: a. providing a wafer; b. processing thewafer; c. detecting a defect on the wafer using the defect inspectionmethod of claim 11; d. repeating necessary times of the steps b and c;e. assembling the wafer into a device.
 13. A defect inspection method byusing an electron beam system as defined in claim 8, further comprising:a step for forming an SEM image by a scanning operation, and thenmeasuring and storing a position of a specific pattern on said sample;and a measuring step for measuring a potential of said pattern byselective scanning or irradiation on said specific pattern; wherein itis examined from a result of measurement of the potential of saidspecific pattern whether or not there is a defect in said sample.
 14. Adefect inspection method by using an electron beam system as defined inclaim 8, comprising: a step for acquiring an SEM image by a scanningoperation; and a step for measuring a potential of a pattern; wherein insaid acquiring step and said measuring step, at least one of anexcitation of said objective lens, a landing energy to said sample and acathode voltage of said electron gun may be changed.
 15. An electronbeam system comprising: an electronic optical system including a primaryoptical system for irradiating an electron beam against a sample and adetecting system for detecting an electron beam emanated from thesample; a movable stage for carrying the sample and moving the samplerelative to said electronic optical system; and a position sensorcapable of measuring a position of the sample by measuring anelectrostatic capacity, wherein said movable stage is moved on the basisof a position signal output from said position sensor so as to bring thesample into a reference position in said electronic optical system witha desired precision, and in the condition where the sample has beenmatched to the reference position in said electronic optical system withthe desired precision, an SEM image of a surface of the sample isacquired by said electronic optical system and thus acquired SEM imageis used to evaluate a fine geometry on the sample surface.
 16. Anelectron beam system according to claim 15, wherein a comparativeevaluation is conducted by applying a pattern matching between saidacquired SEM images or between said acquired SEM image and a referenceimage.
 17. An electron beam system according to claim 16, wherein acomparative evaluation is conducted by applying a pattern matchingbetween the SEM image and the reference image by performing either oneof a translation, a rotation or a magnification tuning of the image. 18.An electron beam system according to claim 15, wherein said primaryoptical system irradiates a plurality of electron beams against thesample, and said detecting system detects secondary electrons emanatedfrom the sample by irradiation of the plurality of electron beamsagainst the sample by a plurality of secondary electron detectors. 19.An electron beam system according to claim 15, wherein a differencebetween an area to be evaluated on a sample surface and a field of viewof the electronic optical system is calculated on the basis of saidacquired SEM image, and thus calculated difference is compensated by adeflector and then the SEM image is acquired.
 20. A device manufacturingmethod comprising the steps of: a. providing a wafer; b. processing thewafer; c. detecting a defect on a processed wafer using the electronbeam system of claim 15; d. repeating necessary times of the steps b andc; e. assembling the wafer into a device.